Process for cooling liquids



Sept. 30, 1941. s. AP. MILLER 2,257,616 l y PROCESS FOR COOLING LIQUIDS med Apri125, 1940 BY ATTORNEY Patentedy Sept. `30,

2,251,616 PROCESS FOR COOLING LIQUIDS Stuart Parmelee Miller, Scandale, N. Y., assignor to The Barrett Com corporation of New Pm. New York, N. Y., a Jersey i Application Api-u z5, ma, serial No. 331,558

-These problems arise from the following conditions: l

a. Large tonnage of material to be handled.

b. Close control of solidiflcationpoint required in nal products.

c. High 'degree of purity required in the more highly rened grades.

d. Diiiculty of complete. removal Iof attendant impurities.

1 claims- (cl. sz-rm naphthalene is increased through loss of yield or necessity for reworking or both, and quality is impaired. i y

Furthermore, when caustic soda or other aqueous solution which it is desired to conserve is employed for the crystallization when it is to be reused, it becomes necessary to remove heat from the solution by some external cooling means. In order to recover a maximum of the naphthalene product' from the crude material,Y it is necessary to .cool the solution to a temperature not far above, or even below, that of the atmosphere. While cooling to around 45 C. under usual weather conditions may be effected readily enough by ordinary heat exchange methods, the cooling problem becomes more difficult as the temperature approaches atmospheric. If only the direct addition of water or aqueous solution at about room temperature, C. for

e. Occurrence of naphthalene in different states of crystal aggregation and tendency to crystallize non-uniformly. l

f. Tendency of naphthalene to form dense and heat-insulating layers of crystals on coolin coils and other cooling surfaces. A

In carrying out prior processes in which crystallization of naphthalene is effected in contact with aqueous solution, it has been diiiicult to obtain the naphthalene product in the form of crystals which may be easily freed of liquid impurities. Thus the naphthalene tends, during crystallization to form certain amounts of crystal clusters or lumps from which the oily impurities cannot readily be removed. Likewise there are formed large numbers of individual crystals or crystal 'aggregates of size considerably smaller than desired; these ne' crystals cause the retention by capillary attraction of unsatisfactorily large amounts of liquid hydrocarbon impurities.

This lack of uniformity of size of naphthalene crystals, as exemplified by presence of lumps or instance, is depended upon to cool the mixture from a temperature of C. down to 30 C., between six and seven times as much cooling solution must be added as there is mixture 'to be cooled. In `View of the dliiiculties involved,

4among which is the large amount of cooling duid required, it' has been unfeasible in many ini stances, especially in warm weather, to effect sufficient cooling to recover more than to of the total contained naphthalene, the balance remaining dissolved in the separated hydrocarbon oil impurities.

Another difficulty encountered in circulating cooling liquid from crystallizing tanks through coolers for reuse is the formation of naphthalene deposits on coils or other cooling surfaces. These deposits result from the further cooling of oil entrained in the cooling liquid on coming in oontact with the cooling surfaces; they adhere to the latter and crystallize, forming a layer of oily `naphthalene crystals which reduces the cooling eiiiciency of the equipment and require periodic removal.

The above discussion applies to the process which is believed to represent, prior to the invention of my said copending application Serial No. 203,116, filed April 20, 1938, the most advanced practice in producing purified or rened naphthalene and which has been operated on a large scale. VIt has been possible to make many desired vgrades of rened control of operations, by some sacrifice of cost and of yield, and by including or adding sulicient purification steps of one sort or another. In the embodiments heretofore available, however, the process has had inherent defects, namely, the very and especially 4 naphthalene by careful if desired may be carried out suitable auxiliaries, thereby doing away with extensive plant required for its operation, the investment in and maintenance'of which constitute a heavy charge on the product, and the impossibility of realizing or approaching closely in practice the yields and quality of naphthalene theoretically possible. I

By operating in accordance with the invention of said copending application, the formation of `undesirably large crystalclusters or lumps and especially of undesirably fine naphthalene crys-r tals or crystal aggregates is avoided, the desirable species of crystal aggregates disclosed in the Gould United States Patent No. 1,448,688 may be obtained, the temperature may without dimculty be reduced sufficiently to recover all the naphthalene practically recoverable, and the operation in one vessel with much of the extensive equipment previously required and correspondingly reducing the necessary investment and maintenance. Since the 4entire crystallization and purification operationmay be conducted in one piece of apparatus, thus and even slower rates ofcrystallizatiomay be,

used when economically feasible. Preferably the rate should be regulated'so that the time y lies between :c x :f5-0 and 90 (As pointed out in the said copending application, the above algebraic expression is applicable in the treatment of crude naphthalene in crystallizers of various sizes andshapesx. Thus the conditions are applicable with crystallizer's having a diameter as small as 5 feet and as large as4 15 feet, and with naphthalene layers having a depth as little as 1 and as much as 12 or 15 feet.

My aforesaid co-pending application discloses that it is preferred to practice the process so that evaporation of the aqueous liquid occurs at o r eliminating several pieces of equipment and l process steps, the opportunities for variation in Y. control and attendant variations in yield and the earlier methods may quality characteristic of be substantially eliminated with the result that I yields and quality of finished product are sharply improved and separated by-product oils are relatively free of naphthalene. i f

While the maior commercial advantages of my process are realized in the refining and purification of naphthalene, in some cases a certain amount of benefit may be derived by using it to convert already purified naphthalene of undesirable physical form into the characteristic type and size oiA crystals described below, without subs'tantial rise in solidication point.

The above results are obtained by extracting heat from a liquefied-naphthalene-aqueous-liquid mixture by evaporatng a part of the liquid therefrom. The evaporation may be effected by reducing the pressure on the mixture to a sufficient extent to cause ebullition at the prevailing temperature without the application of cxternal heat. The aqueous liquid should preferaby have a vapor pressure substantially above that of the naphthalene at the temperatures in-y volved, but this is the case with practically all aqueous solutions having a reasonable degree of dilution, and solutions used in previously known naphthalene crystallization `operations. may be used satisfactorily.

The proper rate of cooling may be obtained by conducting the evaporation so that the time in hours y required to crystallize a weight of actual naphthalene equal to 1% of that originally present in the crude being treated is not less than where :c represents the height in feet of the inf itial layer of the molten crude.

The time y, defined in the above equation, may

be increased very greatly beyond the minimum i limit,

240 l without seriously impairing the quality of the crystals produced; good results canv be obtained 4when higher levelsl causes evaporation of the aqueous'v solution. The said co-pending application also` discloses that in place of the air or gas suitable mechanical'agitators or pumps may be used to 'bring the aqueous solution, preferably in the form of droplets, tothe upper surface of the naphthalene, suitable provision being made for vacuum regulation. There is also disclosed in the said application the carrying out of the process so. that substantial evaporation occurs (a) in the vapor space over the naphthalene, by pumping the aqueous solution from the bottom of the tank to a nozzle or spray head located in the vapor space; (b) at'an intermediate level, by pumping the aqueous solution to a nozzle or distributor head located at a desiredr point between the bottom and topof the naphthalene layer; or (c) at the bottom of the naphthalene layer by not circulating the aqueous solution to higher levels. The choice between modifications (a), (b) and (c) and the preferred process hereinabove described depends largely on the size and shape of the equipment used. As pointed out in the aforesaid co-pending application, ex-

periment confirmed by commercial operation has shown that the process gives smoothest and most satisfactory operation when a'tall crystallizer is used containing a relatively deep layer of molten naphthalene. This is the most compact form of apparatus and most economical of door space.

This application is directed to the modifica-` tion disclosed in said co-pending application involving a crystallizer containing a relatively deep layer or batch of molten naphthalene and involving the circulation of the caustic soda solu- .tion of a specific gravity higher than that of the or in any desired manner.

2,257,616 tained is preferably, but not necessarily, as high eifects agitation thereof with consequent increase in the rate of cooling. Furthermore, it has been found that operation in this manner eliminates bumping which occurs when liquid masses of considerable depth are boiled under vacuum. Upon completion of the crystallization of the naphthalene, the vacuum is broken and the crystalline product is washed with a solvent if a highly purified product is desired. The crystallizer is then opened and the product removed manually The body ofnaphthalen or other liquid to be cooled may be of any desired depth; preferably it is of a depth substantially greater than its diameter, if a cylindrical body is employed, or cross-sectional extent. and may be ofa depth equal to its cross-sectional extent. The point of introduction of the heavier cooling liquid will, of course, vary depending. on the vacuum employed, the depth of the body of lighter liquid to be cooled, the desired rate of cooling, etc. This point of introduction of the heavier liquid should be far enough below the level of lighter liquid so that under conditions of operation it does not flash ed into vapor without effecting substantial cooling of the lighter liquid. .As a general rule, this point of introduction of the heavier liquid is at least about six -inches below the level of lighter liquid to be cooled by evaporation of a portion of the heavier liquid circulated through the lighter liquid.

In the preferred embodiment illustrated on the drawing the invention is shown in connection with a layout of apparatus for crystallizing naphthalene and the present description will be confined to this present illustrated embodiment of the invention.- It will be understood, however, that the novel features and improvements are susceptible to other applications, such as, for example, as the crystallization by cooling of bodies of molten phenanthrene, diphenyl or uorene, by circulating therethrough while maintained under vacuum solutions oi caustic soda. potassium hydroxide, sodium sulfate, sodium chloride or other liquids or solutions immiscible therewith, of higher speciilc gravity and having a higher vapor pressure than the liquids to be cooled, and effecting evaporation of a portion of the circulated heavier liquid' by introducing it continuously at a point not far below the surface of the body oi liquid of lower speelde gravity and permitting vthe liquid of higher specic gravity and vapor pressure to settle through the lighter liquid, or thecooling of such and other lighter liquids in the manner herein described by circulating a heavier liquid having a higher vapor pressure through a body of the lighter liquid maintained under vacuum. Hence,the scope of the invention is not counned to the embodiment herein described.

In the drawing, reference, character l indicates a crystallining tank which may be, for example, in diameter, be provided with a cone bottom 3u deep, contain (measuring from the bottom of the cylindrical portion) a layer of caustic about 4i deep, a layer of molten napthalene about 12' deep, and have a vapor space of substantial extent, say, 3' above the level of the naphthalene. The erystallizer I communicates by means of pipeline E with va. barometric condenser 3, which in turn communicates by means of a pipeline 4 with a steam jet vacuum generator E. A pump 6 has its inlet l communicably connected with the cone bottom 8 of the crystallizer and is provided with a feed line 9 which supplies caustic sodaisolution withdrawnfrom the base oi' the crystallizer to a spray-head l0 disposed beneath the level of the molten naphthalene within erystallizer l. The sprayhead i0 is preferably positioned about 6 beneath the level of the molten naphthalene which may be charged through inlet vii.

A tank l2 is disposed to `:receive from the barometric condenser 3 condensate and caustic,

soda solution circulated through the condenser. This condensate is constituted in part of oil and water evaporated in. the crystallizer. The oil and caustic soda stratify in the tank l2. A portion of the lower layer of caustic soda solution may be passed through valve controlled pipe ltby means of pump 6 to the crystallizer. Water may be added at inlet it; oil removed at valve controlled outlet i5. j

Condensation of vapor in condenser 3 is preferably eiected by direct contact with caustic soda solution which is circulated by means of pump it through line il, connecting the baseit dou/s by gravity through'the barometric leg Ztl into tank it. The circulating system il, it, it, it, through which the caustic soda solution hows is maintained under vacuum by means of line di communicating with pipeline l and thus connecting the vacuum evaporator with the steamv .iet vacuum generator 5.

Loss oil water due to water vapor removed from the circulating system il, it, it and 2b may be compensated by the addition 'of water to the tanlr i2. Tanic it is provided with a vent 2i and a valve controlled inlet 23.

It has long been known that too great a temperature difference between crystallizing naphthalene and cooling liquid in direct contact with it tends to produce large amounts of very small crystals and relatively large crystal aggregates that occlude mother liquor.

in the present process the temperature difference between boiling solution and adjacent naphthalene appears to be infinitesimal, and may be considered as continuously destroyed and reestablished by the crystalliaing and boiling processes respectively. The rate of this transfer f 'higheu the initial purity of the naphthalene, the more rapid the rate of cooling may be toy yield satisfactory results; for example, with a 65 C. solidiilcation-point naphthalene a rate l diicult and time-consuming.

` of per hour is preferred, but with a 13 C. solidication-point naphthalenje a rate of 12% to 13% per hour is preferred.; l p

Because `of the elimination of -undulyy ne crystals and of undesirable crystal clusters in my process, the crystalline product may be further purified to advantage by 'washing it with a solvent, for example. coal-tar naphtha, petroleum naphtha, or iso-propyl alcohol. The wash liquid, in'addition to being a solvent for the oily impurities, preferably is a relatively poor solvent for naphthalene and has :a boiling range suiiiciently differentl from that of naphthalene to permit easy separation by distillation. A` solvent with lower boiling range than that of naphthalene is usually better for the purpose than one with higher boiling range. This washing step removes oil adhering to the crystals after the crystallization. In two crystallizations and drainings followed by coal-tar naphtha washings, I have been able without removal of naphthalene from the apparatus to convert crude naphthalene of 64 solidication point 'into products having soldification points as high as '19.3 C. after removal of the naphtha. This marked rise in solidication point appears due to the precise control of crystal formation, made possible by my invention with consequent efficient removal of oils and other impurities by my'process and is attended by a relatively low accompanying loss of naphthalene as compared with previous processes.

Products may be made from clean commercial crudes by my process of such purity that upon evaporation in air they leave no residue and do not stain cloth materials with which they are brought into contact. As a consequence they may be used directly for such purposes as mothproong garments, whereas in the past the commercial naphthalene products were not suitable for this use until after they had been subjected to further treatment, as washing with sulfuric acid andl subsequent sublimation (or at least to the latter step). y

Water may be added to the crystallizer during the cooling, if desired, to compensate for loss by evaporation and to maintain the aqueous liquid concentration approximately constant.

One of the advantages of the present invention is the fact that it makes possible a ready and complete separationv from the aqueous liquid of oily impurities removed from the naphthalene, and the recovery of such oils as a by-product. Ordinarily the oily impurities accompanying naphthalene in crude naphthalene have a spe,

cific gravity close to that of Water; accordingly, gravity separation of these oils from water is As the aqueous liquid used in the present invention is a. solution having a specific gravity substantially higher lthan that of water these diiliculties are obviated. When it is desired to recover tar-acids directly from the naphthalene crude. as is usu` i ally the case, this solution is preferably a caustic,

soda solution (although caustic potash could also be used). Where it is' not desired to extract taracids from the crude, e. g'. where it is desired to produce a tar-acid oil as a by-product of the naphthalene purification, sodium sulfate or sodium chloride solutions can satisfactorily be used.

Since the temperature obtainable by vacuum evaporation may be lower than the temperature of commonly andeconomically available cooling liquids, I may readily and economically obtain temperatures as low as or `lower than the prevailing atmospheric temperature and thus may Furthermore, since heat is abstracted by faces are done ,away with and the problem of preventing deposits on them is eliminated. Insulation of tank surfaces effectively preventsV crys' talli'zation of naphthalene thereon.

Furthermore, the practice of the process of this invention prevents bumping, which is encountered when liquid masses of considerable depth, say, over 5 feet, are boiled under vacuum. Also, it results in a substantial reduction in the loss of naphthalene, since the cooling takes place from the top of the body of molten naphthalene downwardly, resulting in the subjection of any naphthalene vapors which might tend to escape from the crystallizer to. lower temperatures than would otherwise be the case, with consequent condensation thereof. Cooling in this manner has the further advantage hereinabove pointed out that it increases the rate of cooling, with consequent saving of time. A

It is to be understood that this invention is not, restricted to thepresent disclosure otherwise than as defined by the appended claims.

What is claimed is:

1. The process of cooling 'a pody of liquid by ,vacuum evaporation which Vcomprises adding to a body of substantial depth of said liquid another liquid immiscible therewith and of greater Specic gravity and higher vapor pressure than the first mentioned liquid, maintaining said body under vacuum while withdrawing theiliquid of greater specific gravity and higher vapor pressure therefrom and introducing it into said body to eifect cooling of the body of substantial depth ofl the liquid of lower specific gravity by the evap oration of a portion of the liquid of greater specific gravity and higher vapor pressure.

2. The process of cooling 'a body of liquid ofsubstantial depth by adding thereto a second .liquid of greater specific gravity and higher vapor pressure and effecting evaporation of a portion of the said second liquid, which comprises establishing a body constituted of both of said liquids, with a body of said first-mentioned liquid of substantial depth superimposed on said second-mentioned liquid, withdrawing the liquid of greater specific gravity and higher vapor pressure and recirculating it through said upper body by introducing it near but below the top of said upper body and causing it to settle through said upper body while subjecting said body to vacuum.

- 3. The process of cooling a liquid by adding thereto a second liquid of greater specic gravity and higher vapor pressure and effecting evaporation of a portion of the said second liquid, which comprises establishing a body constituted of both of said liquids of a cross-sectional extent at least about 5 feet and a depth at least equal to the continuously introducing the said portion thus withdrawn at a point not less than about 6 inches below the top of said body, causing evaporation Aof a portion of said liquid of greater specific gravity to take place and thus cool the rst mentioned liquid, and causing the unevaporated portion of i said liquid of greater specic gravity to settle through said body.

4. The process of crystallizing a substance from the-group consisting of phenanthrene, diphenyl, naphthalene and fluorene, which comprises establishing a body of the said substance in liquid condition of substantial depth, maintaining said body under vacuum while introducing near `but below the top of said body a liquid of a specific gravity greater than that of said substance and immiscible therewith, causing evaporation of a portion of said liquid of greater `specific gravity to take place so as to cool the body of said substance to effect crystallization thereof, causing the remainder of said liquid of greater specific gravity to settle through the body of said substance and collect beneath the said body, withdrawing the liquid of greater speciiic gravity thus collected and .continuously recirculating it through the said body until crystallization of substantiallythe entire content of said substance in said body has taken place.

5. The process of crystallizing a substance from the group consisting of phenanthrene, diphenyl, naphthalene and iiuorene, which comprises establishing a body of said substance of a crosssectional extent at least equal to 5 feet and of a 'depth substantially greater 'than the cross-sectional extent, maintaining said body under vacuum, introducing near but below the top of said body a solution of material from the group consisting of caustic soda, potassium hydroxide, sodium sulfateand sodium chloride, of a specific gravity greater than that of said substance, caus ing evaporation of a portion of the liquid of greater speciiic gravity to take place so as to cool the said body to effect crystallization of the said substance, causing the remainder of the said liquid of greater specic gravity to settle through the said body and to collect beneath the said body, withdrawing the liquid of greater specific gravity thus collected and continuously recirnaphthalene of a cross-sectional extent at least equal to 5 feet and of a depth substantially exceeding its cross-sectional extent, .maintaining t said body under vacuum, introducing at about 6 inches below the top of said body a caustic soda solution of a specific gravity greater than that of the naphthalene, causing evaporation of a portion of the caustic soda solution to take place so as to cool the 'body of naphthalene to eiect crys- Vtallization thereof, causing the remainder of said caustic soda solution t0 settle through the body of molten naphthalene and to collect beneath the said body of naphthalene, withdrawing the caustic soda solution thus collected and continu- `ously recirculating it through said body of and the remainder to settle through the body of molten naphthalene, until crystallization of substantially the entire naphthalene content of said body has taken place;

7. The process of crystallizing naphthalene which comprises establishing a body of molten vnaphthalene of substantial depth, maintaining said body under vacuum whiley introducing near culating it through the said body until crystal-A lization of substantially the entire content of said substance in said body has taken place.

6. The' process of icrystallizingI naphthalene which comprises establishing a body of molten but below the top of said body of molten naphthalene a caustic soda' solution of a speciilc gravity greater than that of the naphthalene, causing evaporation of a portion of the caustic soda solution to take place so as to cool the body of naphthalene to eiect crystallizationv thereof, causing the remainder of said caustic soda solution to settle through the body of molten naphthalene and tocollect beneath the said body of naphthalene, withdrawing caustic soda solution thus collected and continuously recirculating it through the said body of molten naphthalene until crystallization of substantially the entire naphthalene content of said body has taken place, and adding water to the body of caustic soda solution beneath thesaid body of naphthalene to replace that' lost by evaporation,

n STUART P. MILLER. 

